Question

why do nonpolar compounds tend to have lower melting points and boiling points than polar compounds?
a. nonpolar molecules have weaker covalent bonds within them.
b. polar molecules have ionic bonds between them.
c. polar molecules have metallic bonding.
d. nonpolar molecules only have van der waals forces between them.

Explanation:

Non - polar molecules are held together by weak Van der Waals forces. Polar molecules have stronger intermolecular forces like dipole - dipole forces or hydrogen bonding (in some cases). Weaker intermolecular forces in non - polar molecules require less energy to break, resulting in lower melting and boiling points. Option A is wrong as the strength of covalent bonds within the molecule is not related to the melting/boiling point difference here. Option B is incorrect as most polar molecules do not have ionic bonds between them. Option C is wrong because polar molecules do not have metallic bonding.

Answer:

D. Nonpolar molecules only have Van der Waals forces between them.